Published in WGN, the Journal of IMO 22:5, p. 167 (1994)
Authors' addresses:
J. Rendtel, Gontardstraiße 11, D-14471,
Potsdam, Germany, e-mail: jrendtel@aip.de;
R. Arlt, Berliner Straße 41, D-14467 Potsdam, Germany, e-mail:
100114.1361@compuserve.com.
Sinsuke Abe (ABESI, 1.58h), Mateja Albreht (ALBMA, 1.05h), Luis R. Bellot (BELLU, 4.73h), Neil Bone (BONNE, 2.00h), Jose Antonio Caceres (CACJO, 4.43h), Ricard Casas Rodríguez (CASRI, 2.18h), Roman Chakarov (CHARO, 8.15h), Bih-Lin Chong (CHOBI, 12.91h), Ren-Yuh Chong (CHORE, 14.59h), Maurice Clark (CLAMA, 14.32h), Peter Craven (CRAPE, 1.00h), Jozef Csipes (CSIJO, 0.88h), Uros Cvelbar (CVEUR, 0.73h), Peter Dalakov (DALPE, 4.99h), Mark Davis (DAVMA, 7.50h), Vincent Devore (DEVVI, 3.67h), Galina Dimitrova (DIMGA, 2.80h), Robert Doe (DOERO, 0.92h), Peter Dolinsky (DOLPE, 2.68h), Phyllis Eide (EIDPH, 10.02h), Tositake Fukuhara (FUKTO, 2.67h), Kai Gaarder (GAAKA, 15.79h), Adrian Galea (GALAD, 3.54h), Atanas Gavrailov (GAVAT, 5.67h), Jaroslav Gerbos (GERJA, 4.81h), Ivanka Getsova (GETIV, 5.35h), Vincent Giovannone (GIOVI, 1.00h), George W. Gliba (GLIGE, 3.00h), Shelagh Godwin (GODSH, 6.99h), José Gomez Castaño (GOMJO, 2.00h), Victor Gonzalez (GONVI, 1.49h), Ian Gray (GRAIA, 4.01h), Keith Green (GREKE, 1.84h), Valentin Grigore (GRIVA, 12.63h), Debbie Harrelson (HARDE, 1.84h), Joy Harvey (HARJO, 9.42h), Takema Hashimoto (HASTA, 7.42h), Yukiti Hattori (HATYU, 3.75h), Paul Haworth (HAWPA, 1.80h), Robert Hays (HAYRO, 1.00h), Lars Trygve Heen (HEELA, 15.69h), Trond Erik Hillestad (HILTR, 13.08h), David Holman (HOLDA, 13.25h), Terry Holmes (HOLTY, 1.33h), Oomi Iiyama (IIYOO, 2.28h), Kiyoshi Izumi (IZUKI, 2.92h), Anne Jokinen (JOKAN, 1.50h), Toshio Kamimura (KAMTO, 1.44h), Petteri Kankaro (KANPE, 1.17h), Fumihiko Kanno (KANFU, 2.82h), Junichi Kasei (KASJU, 5.24h), Kazuko Kawamura (KAWKA, 1.00h), Timo Kinnunen (KINTI, 2.63h), André Knöfel (KNOAN, 1.57h), Matjaz Kosec (KOSMT, 0.67h), Tarou Kuribayasi (KURTR, 4.72h), Taiiti Kurosawa (KURTA, 0.83h), Andrej Lampe (LAMAN, 2.00h), Anna S. Levina (LEVAN, 0.83h), Robert Lunsford (LUNRO, 16.97h), Daniel Marín (MADAN, 2.78h), Katuhiko Mameta (MAMKA, 6.00h), Alicia Mania (MANAL, 12.74h), Krasimir Manov (MANKR, 5.72h), Takuya Maruyama (MARTA, 0.92h), Khalid Marwat (MARKH, 9.12h), Yukihisa Matumoto (MATYU, 6.67h), Alastair McBeath (MCBAL, 16.50h), Tom McEwan (MCETO, 4.01h), Earl Mead (MEAEA, 1.00h), Frank Melillo (MELFR, 2.50h), Javier Méndez Álvarez (MENJA, 7.00h), Vasile Micu (MICVA, 3.88h), Koen Miskotte (MISKO, 2.52h), Robert J. Modie (MODRO, 1.00h), Sirko Molau (MOLSI, 4.66h), Alfonso Murias Núñez (MURAL, 2.38h), Michael Morrow (MORMI, 10.13h), Motoyuki Nakaura (NAKMO, 2.67h), Sin Nakayama (NAKSI, 3.00h), Atanas Nikolov (NIKAT, 8.00h), Masayuki Oka (OKAMA, 10.35h), Hiroyuki Okayasu (OKAHI, 1.50h), T. Oldroyd (OLDT, 1.00h), Diliana Porozhanova (PORDI, 8.44h), Lilia Porozhanova (PORLI, 6.05h), David Preston (PREDA, 1.84h), Joze Prudic (PRUJO, 1.12h), Leo Rajala (RAJLE, 1.13h), Pia Rämä (RAMPI, 1.82h), Martin Rapavy (RAPMA, 4.96h), Pavol Rapavy (RAPPA, 4.91h), Jürgen Rendtel (RENJU, 4.29h), Francisco Reyes Andrés (REYFR, 6.25h), Ian Rigney (RIGIA, 6.18h), Neil Roach (ROANE, 9.30h), Alejandro Rodriguez (RODAL, 2.78h), Paul Roggemans (ROGPA, 7.85h), Tuomo Roine (ROITU, 1.00h), Antonio Rom´n Reche (ROMAN, 1.32h), Angeles Rute Perez (RUTAN, 1.30h), Hiromi Sato (SATHI, 11.11h), Koetu Sato (SATKO, 15.91h), Tatuo Sato (SATTA, 6.64h), Brian Shulist (SHUBR, 7.50h), Yasuo Shiba (SIBYA, 5.09h), Hiroyuki Sioi (SIOHI, 2.50h), James N. Smith (SMIJN, 1.33h), George Spalding (SPAGE, 4.74h), Plamen Stoichev (STOPL, 8.83h), Dmitryi Suchov (SUCDM, 2.75h), David Swann (SWADA, 1.92h), Christoffer Swanström (SWACH, 1.25h), Richard Taibi (TAIRI, 4.02h), Syoiti Tanaka (TANSY, 2.66h), Marko Toivonen (TOIMA, 2.03h), Hiroyuki Tomioka (TOMHI, 3.83h), Simon Tonkin (TONSI, 4.96h), Tuomas Törrönen (TORTU, 1.50h), Dávid Tóth (TOTDA, 3.06h), Josep M. Trigo Rodriguez (TRIJO, 5.27h), Yoshiaki Uyama (UYAYO, 3.67h), Valentin Velkov (VELVA, 8.40h), Roger Venable (VENRO, 4.94h), Robert Vyboch (VYBRO, 1.43h), Chris Watson (WATCH, 1.00h), Roy Watson (WATRO, 1.50h), Vic Winter (WINVI, 7.10h), Jeff Wood (WOOJE, 17.88h), Yasuo Yabu (YABYA, 17.34h), Satiko Yamaguti (YAMSA, 1.50h), Chen Yu (YU CH, 0.83h), and George Zay (ZAYGE, 19.03h).
Due to interference from the Moon, the 1992 Geminids could not be monitored appropriately. Not even 1400 shower meteors were recorded in 1992; too small a number to permit a global analysis. (A raw estimate of the activity showed a maximum of ZHR_max=100±20 at sol=261.9°±0.2° for the 1992 Geminids.) The last comprehensive study of the Geminids presented in this Journal dealt with the 1991 Geminid return. The analysis routines of the Visual Meteor Database (VMDB) were used for investigating both the 1991 and 1992 returns. The present paper regarding the 1993 return is based on 20700 shower meteors seen in 668 observation hours. The analysis routines of the VMDB were also applied to obtain the results presented in this paper.
The observations in 1993 concentrated around the maximum. Although a good profile was obtained for the period between December 12 and 15 no reliable r-value could be found for the days before and after this period. The first and last value calculated from the 1992 data (at sol=260.44° and sol=262°31, respectively) turned out to be almost identical with the figures for the same position in 1991. Therefore, we used the r-profile of 1991 (Figure 1 and Table 1 in [2]) to complete the 1993 values since the population index is necessary for computing the hourly rates. The values added are at sol=259.0° with r=2.7±0.1 and at sol=264.0° with r=2.5±0.1. The profile is shown in Figure 1. The entire profile is smooth with no significant variations, and shows the same general shape as in 1991. Centered at the rate maximum of the shower, the population index r reaches its lowest value. However, the difference in r-value between the center and the outer parts of the Geminids is lower than for other major showers (Perseids 1991 and 1992: r=2.9--1.9 [3]; Quadrantids 1992: r=3.7--2.1 [4]). This emphasizes the unique constitution of the Geminid meteoroids [5]. This is also obvious in the small portion of Geminid meteors showing train phenomena compared to particularly the Perseids.
ZHR = n r^(6.5-lm) F / (T_eff cos z)
where n is the number of Geminids and lm, F, and T_eff are the limiting magnitude, field correction, and effective duration of the observation, respectively. The angle z is the zenithal distance of the Geminid radiant.
Figure 1 - Profile of the population index r of the 1993 Geminids. The values at sol=259.0° and sol=264.0° were added from the profile of 1991 as the 1993 data did not yield a reliable result.
Table 1: The population index r of the 1993 Geminids
| Sol (2000.0) | Obs | Geminids | r | lm |
|---|---|---|---|---|
| 259.00 | 4 | 155 | 2.70±0.10 | 5.94 |
| 260.44 | 16 | 1157 | 2.38±0.06 | 6.44 |
| 261.26 | 52 | 6086 | 2.31±0.04 | 6.31 |
| 262.03 | 92 | 11001 | 2.27±0.03 | 6.29 |
| 262.31 | 56 | 5923 | 2.28±0.04 | 6.29 |
| 264.00 | 2 | 102 | 2.50±0.10 | 6.25 |
Table 2: Intervals for the averages of the Geminid ZHRs.
| Period | Interval length | Interval shift |
|---|---|---|
| 250.00-260.50 | 2.00 | 1.00 |
| 260.50-261.55 | 0.60 | 0.30 |
| 261.55-261.70 | 0.40 | 0.20 |
| 261.70-262.50 | 0.20 | 0.10 |
| 262.50-263.00 | 0.50 | 0.25 |
| 263.00-270.00 | 2.00 | 1.00 |
The individual ZHR values were averaged over bins given in Table 2. The averages were weighted by the reciprocal correction factor cos z / (r^(6.5-lm) F).
The choice of the intervals and their lengths depends on the shape of the profile and the number of observational data. Still, many observers concentrate on the near-peak period only. In order to derive a complete profile, Geminid data are required for the entire activity period. Because of the lower numbers of shower meteors, even more intervals would be necessary to obtain good values of r and certain averages of the ZHR. On the other hand, the variations of r and rates seem to be negligible in these branches, and we may average over longer intervals than near the maximum. The choice of the intervals requires us to calculate a first, rough profile, from which the most appropriate splitting is taken.
Figure 2 - ZHR-profile of the 1993 Geminids. The values are given in Table 3. The maximum ZHR of 130±8 occurs at sol=262.1°. The profile is skew as theoretically calculated by Fox et al. [6]
Figure 3 - Detail of the ZHR-profile around the maximum of the 1993 Geminids. In the period between sol=261.8° and sol=262.3° the ZHR exceeds 100. This may be regarded as a kind of ZHR plateau with relatively small rate variations. When averaging the ZHRs, the procedure rejects outliers which lie off the mean by more than 1.645 sigma, i.e., values which lie outside a confidence interval of 90%.
In recent analyses, we tried to compensate systematic errors by deriving personal perception coefficients. These factors were obtained from the average offset of one observer's rates from the mean ZHR in certain periods. The periods should show relatively constant activity or, at least, a monotonic behavior with a slight slope. The 1993 Geminid data concentrated near the maximum; there is little chance to find a period fulfilling the above criteria. We are actually dealing with slopes in both directions. Other periods would include a tiny minority of the observers participating. Therefore, we did not apply perception coefficients to the activity profile. This again underlines the necessity to not restrict observational efforts to the maximum night, but to cover also the other periods.
In Figure 2, we show the complete activity profile obtained from the 1993 observations. The shape of the profile looks very much like the theoretical profile calculated by Fox et al. [6]. Furthermore, it is smoother than the 1991 profile [2]. This may be partly due to the above described effects of the perception coefficients. Figure 3 clearly shows that there is a period of several hours length in which the high ZHR varies rather little. This kind of plateau has been found in previous analyses as well (e.g. [2]). %
Table 3:ZHR-profile for the 1993 Geminids. The Geminid rates based on the r-values given in Table 1. Int. gives the number of available intervals, GEM lists the number of Geminid meteors included in the respective sample. For comparison, the number and hourly rate of sporadic meteors in the same intervals is given as well. r refers to the used population index for the intervals and is interpolated from the profile determined first.
| Sol. (2000.0) | Int | Gem | ZHR | Spor | HR | lm | r |
|---|---|---|---|---|---|---|---|
| 255.154 | 11 | 27 | 4.4±1.6 | 96 | 16.6 | 6.12 | 2.70 |
| 255.519 | 25 | 54 | 4.2±0.8 | 198 | 16.1 | 6.02 | 2.70 |
| 255.947 | 19 | 37 | 4.1±0.7 | 142 | 16.8 | 5.92 | 2.70 |
| 257.632 | 15 | 62 | 8.8±2.3 | 155 | 21.6 | 6.04 | 2.70 |
| 258.569 | 29 | 158 | 8.8±1.6 | 336 | 18.0 | 6.51 | 2.69 |
| 259.791 | 102 | 1072 | 17.5±1.7 | 883 | 14.0 | 6.33 | 2.51 |
| 259.974 | 84 | 971 | 20.1±1.9 | 681 | 13.6 | 6.24 | 2.46 |
| 260.724 | 42 | 731 | 39.2±3.7 | 413 | 22.0 | 6.23 | 2.35 |
| 260.871 | 87 | 2583 | 53.7±3.8 | 900 | 19.5 | 6.24 | 2.34 |
| 261.146 | 82 | 3737 | 68.2±4.1 | 987 | 17.7 | 6.28 | 2.31 |
| 261.341 | 43 | 2224 | 72.2±5.7 | 559 | 17.1 | 6.31 | 2.30 |
| 261.503 | 6 | 339 | 77.0±12.4 | 59 | 13.3 | 6.35 | 2.30 |
| 261.622 | 9 | 376 | 81.5±9.9 | 111 | 24.2 | 5.96 | 2.29 |
| 261.791 | 12 | 573 | 104.4±17.2 | 203 | 36.0 | 6.54 | 2.28 |
| 261.861 | 36 | 1460 | 111.0±9.2 | 477 | 35.1 | 6.49 | 2.28 |
| 261.968 | 86 | 2960 | 126.9±7.0 | 625 | 22.7 | 6.23 | 2.27 |
| 262.039 | 118 | 4031 | 126.4±6.5 | 663 | 17.1 | 6.13 | 2.27 |
| 262.135 | 109 | 3834 | 131.1±8.3 | 554 | 15.1 | 6.20 | 2.27 |
| 262.212 | 70 | 2747 | 131.8±10.2 | 414 | 15.3 | 6.20 | 2.27 |
| 262.323 | 23 | 1204 | 93.9±7.5 | 210 | 15.9 | 6.15 | 2.28 |
| 262.418 | 11 | 483 | 85.3±7.7 | 85 | 14.6 | 6.26 | 2.29 |
| 262.461 | 4 | 96 | 89.9±6.1 | 43 | 38.9 | 6.10 | 2.30 |
| 262.614 | 31 | 931 | 66.7±10.2 | 500 | 28.0 | 6.37 | 2.31 |
| 262.732 | 66 | 1593 | 54.3±4.4 | 955 | 27.7 | 6.37 | 2.33 |
| 262.832 | 36 | 690 | 41.5±2.3 | 465 | 27.6 | 6.35 | 2.35 |
| 263.770 | 15 | 95 | 13.0±2.7 | 219 | 31.2 | 6.40 | 2.45 |
| 264.029 | 22 | 111 | 9.6±2.0 | 333 | 29.6 | 6.39 | 2.47 |
| 265.075 | 17 | 34 | 4.1±0.8 | 180 | 22.5 | 6.12 | 2.50 |
| 265.642 | 14 | 31 | 3.8±1.0 | 110 | 13.0 | 6.28 | 2.50 |
| 266.198 | 4 | 13 | 3.0±1.3 | 44 | 9.4 | 6.64 | 2.50 |
The peak ZHR is 130±8, and is thus somewhat higher than the peak rates observed in the previous years. For comparison, in 1991 a maximum ZHR of 110±10 was observed at sol=262.3°[1]. The shape of the profile is very similar to the theoretical profile derived by Fox et al. [6].
We found that the introduction of perceptions derived from near-peak intervals only is not appropriate. On the contrary, these perceptions may lead to apparent structures. Perhaps this happened in the 1991 analysis [2], where a more rough profile has been derived after the perceptions were included. A revision of the detailed data may bring further light into the application of the perception coefficients.
We urgently ask all observers to watch the shower also in the nights before and after the maximum. We know that December nights are not the most pleasant ones to sit outside -- but it will be worth the effort. The last conclusion, however, holds for each shower for which a profile analysis is intended.
[1] Koschack R., Rendtel J.: Determination of Spatial Number Density and Mass Index from Visual Meteor Observations (II). WGN 18:4 August 1990, pp. 131-135
[2] Rendtel J., Arlt R., Brown P.: The 1991 Geminid Meteor Shower. WGN 21:1 February 1993, pp. 19-28
[3] Koschack R., Arlt R., Rendtel J.: Global Analysis of the 1991 and 1992 Perseids. WGN 21:4 August 1993, pp. 152-167
[4] Rendtel J., Koschack R., Arlt R.: The 1992 Quadrantid Meteor Shower. WGN 21:3 June 1993, pp. 97-109
[5] Halliday I.: Geminid Fireballs and the Peculiar Asteroid 3200 Phaethon. Icarus 76, 1988, pp. 279-294
[6] Fox K., Williams I.P., Hughes D.W.: The Rate Profile of the Geminid Meteor Shower. Mon. Not. R. astr. Soc. 205, 1983, pp. 1155-1169